In the irrigation of certain plants, such as grapevines and avocado trees, there are a number of alternative methods of irrigation, two of which are drip irrigation and mist irrigation. Drip irrigation applies a steady drip water at various locations in the area being irrigated. Drip irrigation often comprises a plurality of pipes traversing the area being irrigated, either on top of the ground or subterranean, with the pipes being punctured and having drip emitters to cause a slow steady outpouring of drips at each of the emitters. While drip irrigation is often useful, it has some disadvantages. For example, because the water is being directly deposited into the ground or on the ground, it does not spread very far from its original point of application.
Mist irrigation has often been used as an alternative to drip irrigation. In mist irrigation, mist emitters extend from elevated pipes, which can be four inches to a foot or more above ground, or sometimes very close to the ground. A mist emitter has a head that throws out water into the air as a fine mist. Some advantages of mist irrigation over drip irrigation are that a large relatively wet area can be attained from a single mist head, especially when the mist head is quite far off the ground, and that a visual indication of whether the emitter is working is provided. Since mist emitter heads sometimes become plugged up quite easily, such a clogged condition is readily observed because a dry spot is visible instead of a wet patch.
A typical prior art mist emitter comprises a long slender tube coupled to a water source and terminating in an emitter head. FIG. 2 illustrates a prior art mist emitter head 14a. Emitter head 14a includes an inlet end 16a with a threaded exterior surface which connects to inlet tubing extending from a water supply conduit. Water passes through the inlet end 16a and exits emitter head 14a through a smaller diameter outlet opening or pinhole 18a. A deflector disc 20a is spaced from the outlet opening 18a and held at a fixed distance therefrom by a connecting post 22a, which also functions as a splitter bar to divide the water flowing from the head. A plurality of teeth 24a extend downward from the periphery of deflector disc 20a. As water flows out of outlet opening 18a it impacts against the bottom surface of deflector disc 20a and forms a mist-type sheet of water spraying radially outward. Teeth 24a reform the sheet into a plurality of streams to direct the water radially outward a further distance. For a given water pressure, mist emitter head 14a operates at a single precipitation rate. To vary the precipitation rate of the mist emitter 14a, a different head with a different diameter outlet opening 18a is utilized.
The problem with mist emitters of this type is that different plants require different precipitation rates. The primary way of varying the precipitation rate is to change the diameter of the pinhole. To do this, a relatively large variety of different mist heads, having different diameter holes, must be stocked. Moreover, because the pinhole is quite tiny, it tends to clog up. Thus, a filtered water supply is required in most mist irrigation systems.